Safety switch for motion picture projecting machines



March 1, 1932. T. T. ALLEN ET AL 1,847,075

SAFETY SWITCH FQR MOTION PIGTURE PBOJECTING MACHINES Filed June 18, 1928 2 Sheets-Sheet 1 INVENTORS: flan/151' Align flariesjfaimcffi Gibbs,

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/ ATTORNEY March 1, 1932. 'r. "r. ALLEN ET AL 1,347,075

SAFETY SWITCH FOR MOTION PICTURE PROJECTING MACHINES Filed June 18, 1928 '2 Sheets-Sheet 2 I llll IIIIIII um r Mi n" 2 if);

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ATTORNEY in LA- Patented Mar. 1, 1932 UNITED STATES PATENT QFFICE THOMAS TWALDEL ALLEN AND CHARLES KENNETH GIBBS, 0F PHILADELPHIA, PENN- SYLVANIA, ASSIGNORS TO .SENTRY SAFETY CONTROL CORPORATION, OF PHILA- DELPHIA, PENNSYLVANIA, A CORPORATION OF DELAWARE SAFETY SWITCH FOB.- MOTION PICTURE PEOJECTING MACHINES 7 Application filed June 18; 1928. Serial No. 288,377.

This invention relates to safety appliances for motion picture projecting machines and more particularly to stop mechanism for dropping the dowser plate to obstruct the rays of light from the arc and for stopp ng the film feeding motor when the film 1S belng fed across the aperture at less than a predetermined rate of speed.

Various devices have been provided for operating the dowser and stopping the motor of projecting machines and these devices have been placed at various points and are operated by the looping or failure of the film. As the object in motion picture machines is to provide for the proper passage of the film across the aperture, since it is at that point that the ignition will take place if the film moves too slowly, it seems logical that safety mechanism acted upon by the film at, or as jnear as possible to the aperture would be the most sensitive and give the most desired results from the standpoint of fire prevention.

The object of the invention therefore is to provide stop mechanism which will act to 1: stop the motor which feeds the film and will drop the dowser to out off the rays of light from the arc to the film whenever the passage of the film across the aperture drops to less than a predetermined speed.

According to the invention, the mechanism is mounted on the aperture plate and consists of a shaft having sprockets adapted to engage the film and a centrifugal actuating member located on or operated by said shaft,

:12; and contacts open when the speed of the film is at or above a predetermined rate and which are adapted to be closed by the centrifugal actuating member when the speed of the film drops below a predetermined rate.

The drawings illustrate an embodiment of the invention and the views therein are as follows Figure 1 is a front view of a part of a motion picture projecting gate with the improved safety switch mounted thereon,

Figure 2 is a longitudinal sectional view of the same,

Figure 3 is a horizontal section of the same,

Figure 4 is a cross-section taken on the line 9-9 of Figure 1,

in each of the figures like reference characters indicate like parts.

In illustrating the invention it has been deemed unnecessary to show any part of the projecting machine other than that necessary for the explanation of the invention. Consequentiy, same has been omitted.

The projector is provided with a gate 10 carrying an aperture plate 12. The gate is ordinarily provided with a pair of guide rollers (not shown) and these have been replaced by sprockets lat which engage the perforations in the edges ofthe film in the same manner as do the regular sprockets of the projector.

These sprockets are mounted on a shaft 16.

For the purpose of this invention the shaft is extended and is provided with a centrifugal device enclosed in a casing. This casing is secured to the housing for the bearing 18.

The switch which is mounted on the wings 25 which are fastened to the gate as shown in Figure 1. The shaft is provided with an auxiliary bearing 71 which is provided with a. flange?" 2 and this flange is fastened to the end member 73 of a casing 7 1 by the screws 76 shown in Figure 8. The end of the shaft 16 extends through the bearing 71 and is provided with a disk 77 which has a collar 78 which is driven onto the end of the shaft so that said disk is rotated by the shaft. This disk is provided with 'a pair of fly weights 79 which have a reduced portion 81 as shown in Figure 11 and are pivoted at the reduced portion by screws 82 passing through the holes IOU oppositely extending spring contact arms 93 and 94. These arms are each mounted at one end on separate binding posts 96 and their free ends are adapted to make contact with contacts 97 mounted on said post.

The friction drum is provided with a pin 98 for the purpose of holding one end of a spiral spring 99 and the other end of the spring is fastened onto a pin 190 on the bracket 86. The cam 92 has oil'set faces 101 on two diagonal corners of the same which form seats for the spring contact arms 93 and when the cam is turned a sufficient amount.

The casing 74, partition 89 and cam 92 are all formed from electrical non-conducting material such as bakelite or the like. The binding posts 96 are of course adapted to receive electric wires 59 and 64: for connecting the switch into the electric circuit.

The operation of this switch is as follows WVhen the film is passing over the aperture and is operating the shaft 16 by the sprockets 14 thereon engaging the perforations at the sides of the film, the disk will turn with suilicient velocity to throw the pivoted fly weights out centrifugally and as they come in contact with the inner face of the friction drum, they will frictionally turn the drum slightly and thus turn the cam 92, thereby spreading the spring contact arms 93 and 94- and opening the contacts 97. This will of course open the switch.

If, for any reason, the speed of the machine, or rather the passage of the film over the aperture, falls below a certain set and predetermined rate, the fly weights will not bear against the friction drum with sufficient friction to retain the cam in its open contact position and the cam will thus be turned around and the contacts closed.

The snappy action of the switch is increased by the offset portions 101 because as the cam is rotated, it will seat itself by these offset portions onto the spring contact arms 93 and 9s; and when, for any reason, the speed of the film falls below the required rate, the action of the spiral spring 99 will snap the cam drum back to its original position and. close the contacts 97.

Of course, the switch illustrated may be modified in Various ways without departing from the invention herein set forth and hereafter claimed.

The invention is claimed as follows l. A safety switch for motion picture projecting machines comprising a shaft having sprockets for engagement by the film, a switch comprising centrifugal fly weights mounted on said shaft, a friction drum adapted to be frictionally engaged by said fly weights, a cam 011 said drum, and contacts adapted to be opened and closed by said cam.

2. A .safety switch for motion picture projecting machines comprising a shaft having sprockets for engaging the film, a switch comprising friction means mounted 011 the end of said shaft, a casing, a cam drum within said casing and arranged to be engaged by said friction means, a cam on said drum, and contacts arranged to be opened and closed by said cam.

3. A safety switch for motion picture projecting machines comprising a shaft having sprockets for engaging the film, fly weights mounted on the end of said shaft, a casing, a friction drum in said casing and arranged to be friction-ally engaged by said fly weights, a cam on said drum and in said casing, and contacts in said casing arranged to be opened and closed by said cam, depending upon the speed of said shaft.

In testimony whereof we have signed our names to this specification.

THOMAS TWVADDEL ALLEN. CHARLES KENNETH GIBBS. 

